High-pressure studies on the coacervation of copoly(N-vinylformamide–vinylacetate) and copoly(N-vinylacetylamide–vinylacetate)

The effects of pressure on the temperature-induced coacervation of copoly(N-vinylformamide–vinylacetate) and copoly(N-vinylacetylamide–vinylacetate) in aqueous solution were investigated by measuring the apparent light scattering, and the effects of the concentrations of polymer and inert salt were also studied. At lower pressures, the apparent temperature of transition, T _c, increased with an increase in the pressure, but further increases in pressure decreased T _c. In contrast, the apparent pressure of transition, P _c, monotonously increased with decreasing fixed temperature. The T–P diagram was elliptical, but the curvature was not large and extrema were not observed in the low-temperature and high-pressure range. Anions with low lyotropic numbers induced an almost linear decrease in the T _c and P _c, whereas anions with a high number increased the T _c and P _c. In both polymers, the T _c and P _c depended on the concentrations of the polymers, reflecting the association/aggregation mechanism of coacervation. This is in contrast to typical thermoresponsive polymers such as poly(N-isopropylacrylamide) and poly(N-vinylisobutyramide), which show the coil-collapse transition as a single molecular event.